There is a growing trend in the development of non-invasive methods for detection and characterization of tumors. As a second most common cause of cancer-related death in men, prostate cancer is a usual object for many research studies. The appropriate tumor localization and staging are very important for determining the best choice of treatment. The most common diagnostic methods for prostate cancer are transrectal ultrasound and conventional magnetic resonance imaging (MRI). Unfortunately, these methods are not always able to differentiate and characterize the cancerous and healthy prostate tissues.
A comparatively new method for characterization of tumor microvasculature is the dynamic contrast enhanced (DCE) MRI. Originally developed to describe the blood-brain barrier permeability, DCE MRI was later used to help identify breast lesions as being malignant, benign, and so forth. The non-invasive DCE-MRI is very helpful not only for initial and early diagnosis, but also for painless follow-up treatments.
For DCE-MRI, the multi-slice images are acquired before, and during, contrast agent infusion. Subsequently, signal intensity versus time curves are analyzed using appropriate models for quantitative assessment of permeability and microvasculature of healthy and cancerous tissues. Those models rely on pixel-by-pixel analysis and high-spatial resolution of images, which are necessary to avoid volume averaging of contrast enhancement patterns. However, the high-spatial resolution poses some limitations on temporal resolution (i.e., how fast images can be taken). In some tissues with slow dynamic of contrast agent (e.g., in breast tissue), the usual temporal resolution achievable in most dynamic contrast enhanced (DCE) MRI exams is sufficient for accurate and reliable pharmacokinetic analysis and calculation of resulting parameters, such as vascular permeability (k-trans) and extracellular space or volume (V).
However, dynamic imaging in general, and pharmacokinetic methods in particular, may not provide sufficient temporal resolution to monitor the rapid dynamics of the contrast agent exhibited in fast-enhancing tissues such as prostate tissue. This is particularly true for the majority of currently deployed MRI scanners, which have limited gradient strength and cannot perform sequences fast enough. Moreover, some improvement of spatial resolution of prostate tissue can also be obtained using an endorectal coil. However, this approach has been avoided because of patient discomfort.